1. Field of the Invention
The present invention relates to a process best suited for producing silicon-containing deposition films, particularly amorphous silicon (hereinafter denoted by a-Si) or polycrystalline silicon deposition films useful as photoconductive films, semiconductor films, insulation films or the like.
2. Description of the Prior Art
It is known that a-Si deposition films are formed, for example, by utilizing glow discharge deposition process or thermal energy deposition processes using a raw material SiH.sub.4 or Si.sub.2 H.sub.6. That is, as is well known, SiH.sub.4 or Si.sub.2 H.sub.6 is excited and decomposed by applying electric or thermal energy, forming a-Si deposition films on substrates and utilizing these films for various purposes.
However, in the glow discharge deposition process using SiH.sub.4 or Si.sub.2 H.sub.6 as a raw material, the film during deposition under high output is much influenced by the discharge energy so that it is difficult to keep the film forming system under reproducible and stable conditions. In particular, this is remarkable in the formation of large and thick deposition films.
In the thermal energy deposition process the high operation temperature required will restrict the kinds of the employable substrates and will raise the probability of elimination of useful bound hydrogen atoms from the a-Si deposit, thus making it difficult to attain desired characteristics of the deposition film.
As stated above, when deposition films are formed by these methods using SiH.sub.4 or Si.sub.2 H.sub.6, difficulties remain unsolved in securing the constancy of electrical and optical characteristics and quality of the films and in eliminating irregularities on the film surface or defects in the film interior which are liable to develop during the deposition.
Such being the case, an a-Si deposition method applying light energy to a starting material SiH.sub.4 or Si.sub.2 H.sub.6 has been proposed recently to solve these problems and it is attracting attention. According to this deposition method employing light energy (hereinafter referred to as the "optical CVD process"), the above noted difficulties can markedly be diminished to on account of advantages of this process such as a low temperature permitted at the production of a-Si deposition films. However, since the optical CVD process utilizes a relatively low level of energy, i.e., light energy for the excitation of the starting material SiH.sub.4 or Si.sub.2 H.sub.6, not much higher efficiency of the decomposition can be expected. Thus the optical CVD process encounters another problem such that the improvement of film forming speed cannot be expected and there are difficulties in mass production.